Fungi-eating plants cooperate with flies for reproduction

Fungal-eating orchids were first found offering their flowers to fungus-eating fruit flies for pollination, the first evidence of nursery pollination in orchids. This unique new plant-animal relationship signals an evolutionary shift toward mutual symbiosis.

Orchids have been known to trick their pollinators into visiting flowers by mimicking food sources, breeding grounds, or even mates without offering anything in return. The fungus-eating, non-photosynthetic orchid is no different: to attract fruit flies (Drosophila spp.), the plants typically emit an odor reminiscent of their common diet of fermented fruits or decaying mushrooms.

Fruit flies are attracted to flowers, are trapped there for a short time and stick pollen on their backs, which they then transfer to other plants of the same species. Thus this deceptive relationship offers benefits to only one partner.

Kobe University plant biologist Soutsugu Kenji, who specializes in these orchids, notes that a certain species of this genus, Gastrodia foetida, has particularly fleshy petals that loosen and fall off a few days after pollination. He decided to investigate these plants for the first example of orchids practicing “nursery pollination,” a plant that provides a breeding ground for its pollinator.

And indeed in the study now published in the journal EcologyHe stated that fruit flies often lay their eggs in the flowers of plants and that their larvae can fully develop into adult flies in this environment.

“The most interesting aspect is that, contrary to its common name as a fruit fly, fruit flies, which are a species that specialize in feeding on mushrooms, mostly use decaying Gastrodia foetida flowers as brood sites,” says Sutsugo. A possible explanation is the fact “that Gastrodia foetida is an orchid.” They do not photosynthesize and feed on fungi. These non-photosynthetic orchids often display a chemical similarity to the fungi that ingest them, confirming the old adage “you are what you eat”.

“As a plant that feeds on mushrooms, it is likely that G. foetida tastes similar to mushrooms, making it a prime target for the mushroom-specific fruit fly.” This discovery is significant because it reveals a new type of incubation pollination system, beyond the deceptive strategies commonly found in the genus.

The researcher at Kobe University further explains that the relationship is neither obligatory nor specific, meaning that fruit flies also lay fully-developed eggs on fungi. Thus, this result may represent an example of a transition from a paraphilic relationship towards mutual symbiosis, which is suggested by two factors: the low cost of the plant, in which the petals are no longer needed after pollination; and that the closely related Gastrodia mostly used a deceptive strategy without providing incubation.

Suetsugu concludes, “This study represents the first evidence of nursery pollination in orchids, which, with nearly 30,000 species, are the most diverse plant group in the world. In addition, it contributes to a vital understanding of the complex and mutually beneficial relationships that can evolve.” In “Understanding how plants can provide real benefits rather than simply deceiving pollinators could influence the broader study of plant-animal interactions and their evolutionary dynamics.”